The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air from the tire's inner air chamber. It is often referred to as an innerliner. Rubbers, such as butyl and halobutyl rubber, which are relatively impermeable to air are often used as the major rubber component in the innerliners.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
Halobutyl rubber is generally one of the most expensive rubbers used in a tire. Given the competitive tire market and the continued need to lower the cost of manufacturing tires without sacrificing properties, there exists a need to eliminate or substantially decrease the cost of innerliners which perform such an important function in the performance of a tire.
Emulsion and solution polymerized styrene butadiene rubbers are commonly used in the tread portion of a tire. Since such styrene butadiene copolymers are typically more economical than halobutyl rubbers, one would hope that such styrene butadiene copolymers could be utilized in other components such as an innerliner. Unfortunately, typical styrene butadiene copolymers suffer from unacceptable air permeabilities. Since a rubber used in an innerliner must have acceptable air permeability, the use of a significant amount of styrene butadiene copolymer in an innerliner would be expected to meet with failure.
As can be appreciated by one skilled in the art, another critical property that an innerliner must exhibit is cold flexural properties. Simply stated, since an innerliner will be subject to low temperatures in use and that such temperatures along with the normal deformation of the innerliner lead to cracks, the elastomeric composition must exhibit cold flexural properties to avoid cracks and therefore air leaks.